Best way to get those gems (Iam now at 105, got like 75 from start):
Do the story, join to random multirooms and use your energy?
I'd do co-op until they stop giving you free pearls. You can get 110 pearls through that method before it stops handing them out to you. You can just join co-op and don't need to host yourself, just try a scroll/ramen daily or whatever. I'd help you grind the pearls, but unfortunately you'd only get one set from me before it stopped handing them out. If it was for EVERY co-op, I'd just keep hosting stuff for you to join, but it doesn't work out that way. :/
At that point, I'd move onto the story mode and start clearing it. You get five pearls for clearing each chapter. You get more on Hard mode, but that might be too much for people just starting out. You also get one pearl per map if you manage to get all of the lucky drops, but you'll want a max luck character to farm those so your stamina would probably be better spent elsewhere. I believe there's also a set of Limited Time missions going on for the anniversary that gives you pearls for every ten ranks you increase, which should add up quickly given how easy it is to rank up in the beginning.
Here's a pearl guide I found on Reddit:
https://www.reddit.com/r/NarutoBlazing/wiki/pearlsguide
BTW, I should mention the new Sasuke is great too, but for those starting out, So6P Naruto is a much better choice, given his utility. He'll last you a long while, and will be viable in pretty much any/all game modes. He's a God.
Edit: I was thinking, if the story missions get too difficult, you could always add me and I could co-op with you to get you through them. I'd host, but I'm not sure if you'd get credit for it or not if you're not the one hosting. Also, if you don't host, I don't believe you get rank XP, which you want right now, due to those Limited Time missions. See how things go, not sure what your current roster is. The SM Naruto they give out during the anniversary is pretty nice though, so he should get you a decent ways.
Edit: Sorry, I don't mean to turn this into a Naruto: UNB thread, but I thought I'd also mention, DO NOT FINISH THE ROOKIE MISSION UNTIL YOU FARM MULTIPLE BODY SAKURA! She's insanely helpful, even more so when you unlock all of her abilities/lower her cost by fusing duplicates into her. She also goes up to 80 Luck, which is great for new accounts to start farming lucky drops, as Impact bosses might be too much for you for a while. The stamina needed to acquire multiple of her is low and it's easy to complete. Just do the first stage of the Rookie Trial over and over again until you finish her off (you need to evolve her from 4* to 5* to unlock her final ability). I farmed three of her at 5* personally, with all abilities unlocked. So worth it.